The present invention relates to cutting machines of the type used for cutting pattern pieces from single of multi-ply layups of sheet material. More particularly, the present invention is concerned with a roller guide for controlling the positioning of a reciprocating cutting blade suspended in cantilevered fashion above the sheet material while the blade is advanced along predefined cutting paths.
Cutting machines for cutting pattern pieces from multi-ply layups of sheet material have been in existence for some time. U.S. Pat. No. 3,955,458 issued on May 11, 1976 and having the same assignee as the present invention illustrates one such cutting machine having a reciprocating cutting blade suspended in cantilever fashion over a support table on which the sheet material is held in a spread condition during cutting. The cutting blade is an elongated, thin, flat blade having a sharp, leading cutting edge which is advanced through the layup along predefined cutting paths at the periphery of the pattern pieces. During cutting, the blade must be rotated about its axis of reciprocation, or a similar, parallel axis, in order to remain generally tangent to the cutting path at each point. In the referenced patent, the blade is freely rotatable about such axis and is engaged at its upper end and lower or depending end by means of friction guides, usually formed from a tungsten carbide material for extended life, to establish perpendicularity of the blade and sheet material and to control blade orientation.
It has been found that in cutting deep layups of sheet material or even medium layups of relatively tough material such as denim, significant heat is generated due to friction. First of all, there is friction between the sheet material and blade which generates heat. There is also friction between the carbide guides and the blade. Since the guides are generally mounted in a presser foot which slides over the cloth, heat generated between the foot and cloth raises the temperature of the environment of the guides which interferes with heat transfer away from the blade. The increased temperatures of the blade resulting from the several different sources of friction-generated heat adversely affect the ease with which the blade reciprocates through sheet material, and can reach a point where the material is damaged.
During cutting there are also significant loads applied to the cutting blade from the sheet material, and such loads multiply rapidly in magniture when the cutting blade is not correctly oriented and positioned as it moves through the material. Misorientation of only a few degrees creates side loads which can bend or possibly break an advancing blade. Slight torsional twisting of the blade about its longitudinal axis results in the depending tip of the blade being oriented and traveling in a slightly different direction through lower plies of the layup than the mid portion of the blade traveling through the upper plies of the layup. Such twisting, therefore, produces a relatively unstable condition with the different portions of the blade tending to travel in diverging cutting paths. Blade bending or fracture is again the result.
Slight errors in blade positioning and the loads applied to the blade create errors in the patterns being cut and also cause further increases in the heat generated and the loads themselves. As the loads increase, balde bending and twisting increases. Thus, the overall situation deteriorates progressively and results in cutting errors and damage to the cutting blade or other cutting equipment and the material being cut.
It is, accordingly, a general object of the present invention to improve the cutting operations by providing a cutting machine with an improved blade guide for more accurately controlling the positioning of the blade during cutting.